Printing plates



Oct. 17, 1967 G. s. BRAZNELL ETAL 4 PRINTING PLATES Filed Dec. 21, 1964'United States Patent Ofilice 3,347,152 Patented Oct. 17, 1967 3,347,162PRINTING PLATES George Stuart Brazneil, Frontenac, and Stuart 1).Braznell, Des Peres, Mo., assignors to Brace Engraving Company, St.Louis, Mo., a corporation of Missouri Filed Dec. 21, 1964, Ser. No.419,781 8 Claims. (Cl. 101--376) This invention relates to printingplates, more particularly to a flexible preshaped rubber printing plateand a method of making the same.

The invention is particularly concerned with flexible rubber printingplates (i.e., rubber plates having on one face thereof a pattern inrelief of the matter which is to be printed by means of the plate) suchas are mounted on a cylinder of a printing press. Heretofore, suchplates have been conventionally made flat, and hence they do not conformto the curvature of the surface of the printing press cylinder to whichthey are applied. They tend to spring back to their normal fiatcondition, and this-causes considerable problems in printing operations.There have been previous attempts to form rubber printing plates with abuilt-in curvature, but these have contemplated such concepts as use oflayers of different materials and shrink characteristics, and haveinvolved various complications.

Accordingly, among the several objects of this invention may be notedthe provision of a method of making a flexible rubber printing platewhich is preshaped to facilitate mounting on a printing press cylinder;the provision of a method of making a rubber printing plate havingbuilt-in curvature using conventional printing .plate materials; theprovision of a method of making such a plate which is dimensionallystable; the provision of a method of making such a plate in which arubber layer and a flexible dimensionally stable backing therefor areshaped in a single, simple, economical operation; and the provision of aprinting plate so made which is both flexible and preshaped to a curvedconfiguration. Other objects and features will be in part apparent andin part pointed out hereinafter.

The invention accordingly comprises the constructions and methodshereinafter described, the scope of the invention being indicated in thefollowing claims.

In the accompanying drawings in which one of various possibleembodiments of the invention is illustrated,

FIG. 1 is a plan of a so-called master metal engraving;

FIG. 2 is a perspective in half section on line 2-2 of FIG. 1;

FIG. 3 is a section showing how a so-called matrix is made-using themaster engraving;

FIG. 4 is a plan of the matrix;

FIG. 5 is a perspective in half section on line 5-5 of FIG. 4;

FIG. 6 is a view like FIG. 5 showing the formation of rubber printingplate in accordance with this invention, using the matrix of FIGS. 4 and5;

FIG. 7 is a perspective showing the molded printing plate on a shapingmandrel;

FIG. 8 is a perspective showing the printing plate removed from themandrel, and having sticky-back applied thereto on its concave backface; and

FIG. 9 is a, fragmentary perspective in section of the FIG. 8 plate withthe sticky-back on its back face.

Referring first to FIGS. 1 and 2 of the drawings, there is indicated at1 what is referred to as a master engraving. As shown, this consists ofa rectangular metal plate, for example, which has one face routed out asindicated at 3 to provide a desired printing pattern in relief, and aperipheral retaining wall 5 all around the plate For purposes ofsimplified illustration, the printing pattern is shown as comprising aring 7 and three bars 9, 11, 13 The master engraving is made inwell-known conventional manner. It is used to make a matrix 15. It willbe understood that the master engraving 1 may consist of a hard rubberplate instead of a metal plate.

As shown in FIG. 3, the matrix 15 is made using master engraving 1 inconventional manner by packing a thermosetting resin powder as indicatedat 17 into the routed cavity 3 in the master engraving, and covering thefaces of peripheral wall 5 and printing pattern 7, 9, 11, 13 with thispowder to a predetermined depth. The powder may be a phenol-formaldehyderesin powder such as sold under the trade designation Bakeliteconventionally used for making such matrices. A plate 19 ofthermosetting resin is applied over the powder. This plate may be aplate of phenol-formaldehyde resin such as sold under the tradedesignation Bakelite conventionally used for making such matrices. Itwill be understood that a parting compound will usually be applied tothe master engraving to enable the matrix to be stripped from theengraving. Heat and pressure are applied to set and cure the resinpowder and bond it to plate 19, thereby to form matrix 15 havingimpressions in reverse of relief of the printing pattern 7, 9, 11, 13.The impressions or cavities in the matrix 15 are respectively designated7a, 9a, 11a and 13a. FIGS. 4 and 5 show the matrix 15 stripped from themaster engraving 1. It will be understood that matrix 15 may be madeusing a Bakelite plate instead of powder.

As shown in FIG. 6, strips of unvulcanized rubber R are placed over thecavities 7a, 9a, 11a and 13a in the matrix 15. A rubber sheet 21 isapplied over these strips. This sheet 21 is a plain rubber sheet,without any fabric or other reinforcement therein. A suitable partingmaterial is applied to the matrix prior to the application of rubber Rand sheet 21. The rubber used at R and in sheet 21 may have a durometerin the range from 20-80, for

' example.

At 29 in FIG. 6 is indicated a backing sheet of dimensionally stableplastic material, use of a sheet of poly ethylene terephthalate such asthat sold by E. I. du Pont de Nemours & Co. under the trade name Mylarbeing presently preferred. This is a nonwoven material. It ispreliminarily prepared with a coating C on one face of a thermoplasticadhesive. This adhesive may be, for example, one having a solids contentof pigment-reinforced synthetic rubber and synthetic resin with methylethyl ketone as a solvent, such as that sold under the trade namePliobond 20 by the Chemical Division of The Goodyear Tire & RubberCompany of Akron, Ohio. This particular adhesive contains 20% solids andmethyl ethyl ketone. The adhesive is coated on the Mylar sheet (it maybe simply brushed on) and allowed to dry.

The adhesive-coated Mylar sheet 29 is placed over the rubber sheet 21with the adhesive-coated side of the Mylar sheet contacting the rubbersheet. Then, the assembly of the matrix 15, rubber R, rubber sheet 21and the in FIGS. 79 and designated in its entirety by reference.

out of the press, and while the plate P is still hot, it

is stripped from matrix and immediately attached by fasteners 33 (suchas staples) to a forming mandrel 35, as shown in FIG. 7. These fastenershold the plate under restraint. Mandrel 35, as shown, is cylindrical inshape since plate P is ultimately to be used on a cylinder of a printingpress. The plate is attached to the mandrel with the edges thereof whichwill extend axially across the printing press cylinder extending axiallyacross the mandrel. The printing surface of plate P faces away from themandrel and is generally convex inshape while attached to the mandrel.Any suitable cylindrical object may be used as the mandrel. We havefound it convenient to use fiber tubes such as are used as forms forpouring cylindric concrete columns.

In a typical operation as above described, the plate P when taken fromthe press, stripped from the matrix and applied to the mandrel is at atemperature of about 305 F. to 313 F. (the vulcanization temperature ofthe rubber). The plate, while held in curved condition on the surface ofthe mandrel, is allowed to cool to room temperature, or it may bepositively cooled .by putting it in a refrigerator or spraying coldwater on it while on the mandrel. 4

After the plate has cooled, the staples 33 are removed and the plate istaken oif the mandrel. As a result of cooling in curved condition on themandrel, the plate acquires a definite arcuate shape as shown in FIGS. 8and 9. The radius of curvature of the finished plate is somewhat largerthan the radius of curvature of the surface of the mandrel due to atendency of the plate to recover its original flat shape to some extent.This is taken into accountin selecting the mandrel to be used. Forexample, when the radius of curvature of the finished plate P is to beabout seven and one-half inches (to conform to a printing press cylinderhaving about a fifteen inch diameter), then a mandrel having a radius ofcurvature of about three and one-half inches is used. While plate Psprings back to some extent after removal from the mandrel, it stillretains an arcuate shape so that it con- I forms to the shape of aprinting press cylinder when mounted on it, and has no tendency tospring back to a flat condition as in the case of prior flat rubberprinting plates when mounted on a cylinder. The reason for the retentionof curvature'is not fully understood, but we have observed that allowingthe plate to cool while in curved condition on the mandrel definitelyimparts a built-in curvature to the plate.

The finished curved plate P is adapted to be mounted on a cylinder as bymeans of sticky-back 37 (see FIGS. 8 and 9) applied to the Mylar backing29. Sticky-back is a sheet of pressure-sensitive adhesive material whichis adhesive on both faces covered with a protective sheet 39. Thelatter, is peeled off for. adhering the plate to the cylinder. It willalso be understood that a number of plates P may be adhered by thesticky-back to a Mylar carrier sheet, the latter being wrapped tautaround a printing press cylinder. In either case, the plate P, having abuilt-in curvature corresponding generally to the curva- 4 ture of theprinting press cylinder, has no tendency to spring away from thecylinder and remains firmly afiixed by the sticky-back in its properposition on the cylinder. It will be understood that a number of platesP may be adhered by a suitable adhesive to a Mylar carrier sheet insteadof by sticky-back, and it is also within the purview of the inventioninitially to mold a number of rubber plates directly to a Mylar carriersheet in a vulcanizing press, the carrier sheet in the latter caseconstituting the dimensionally stable backing layer for all the platesmolded thereon and bonded thereto. In the latter.

case, the carrier sheet with the rubber plates bonded thereto would becurved around a forming mandrel to i give it a built-in curvatureadapted to that of the printing press cylinder on which it is to beused.

It will be understood that the principles of the invention as abovedescribed are applicable to producing curved made-ready printing plateswhich are formed to provide for pressure differentiation between variousprinting areas on the plate requiring different printing pressures in amanner similar to that disclosed in Braznell et al. U.S. Patent3,103,168.

In view of the above, it will be seen that the several objects of theinvention are achieved and other advantageous results attained.

As various changes could be madein the above constructions and methodswithout departing from the scope of the invention, it is intended thatall matter contained in the above description or shown intheaccompanying drawings shall be interpreted as illustrative and not in alimiting sense.

What is claimed is:

1. The method of making a flexible rubber printing plate with a built-incurvature and having on the printing face thereof a printing pattern inrelief, comprising applying unvulcanized rubber over a matrix having animpression of said pattern in reverse of relief, applying over saidrubber a sheet of relatively thin flexible dimensionally stable backingmaterial having a coating of thermoplastic adhesive on its facecontacting the rubber, applying heat and pressure to simultaneouslycause the rubber to fill the impression in the matrix, to vulcanize therubber, and to effect permanent bonding of the rubber to the backingsheet, stripping the resulting backed rubber printing plate from thematrix and, immediately upon being stripped and while it is still hotfrom the said heating and pressureapplying step, forming it to a curvedconfiguration, and effecting cooling of the plate while holding it underrestraint in said curved configuration.

2. The method of claim 1 wherein the plate is formed tb said curvedconfiguration and held therein during cooling by applying the platewhile hotto a forming mandrel and removably securing it on said mandrelwith the backing sheet against the mandrel.

3. The method of claim 2 wherein the plate is to be applied to acylinder of a printing press, and the mandrel has a cylindrical surfacehaving a radius of curvature less than the radius of the printing presscylinder, the plate being applied to the mandrel with the edges thereofwhich are to extend axially of the printing press cylinder extendingaxially of the mandrel.

4. The method of claim 1 wherein the backing sheet is a sheet ofpolyethylene terephthalate.

5. The method of claim 4 wherein the plate is formed to said curvedconfiguration and held therein during cooling by applying the platewhile hot to a forming mandrel and removably securing it on said mandrelwith the backing sheet against the mandrel.

6. The method of claim 5 wherein the plate is to be applied to acylinder of a printing press, and the mandrel has a cylindrical surfacehaving a radius of curvature less than the radius of the printing presscylinder, the plate being applied to the mandrel with the edges thereofwhich are to extend axially of the printing press cylinder extendingaxially of the mandrel.

7. A printing plate for mounting on a cylinder of a printing press, saidplate consisting only of two layers, one of said layers being a flexiblerubber layer and the other being a backing layer of a dimensionallystable flexible nonwoven sheet plastic material, said layers beinginterfacially bonded, said rubber layer having a printing pattern inrelief on its exposed face, said plate, in its unstressed conditionprior to applicaton to a cylinder having a curvature generallycorresponding to that of the cylinder with the printing pattern on theconvex face of the plate.

8. A printing plate as set forth in claim 7 wherein said sheet plasticmaterial is polyethylene terephthalate.

References Cited UNITED STATES PATENTS Such l01375 Novotny.

Schmutz 101-395 Waters 101-379 Kunetka 101--379 Macy 101--376 Braznellet a1. 101376 Wallenius 101395 ROBERT E. PULFREY, Primary Examiner. I.A. BELL, Assistant Examiner.

7. A PRINTING PLATE FOR MOUNTING ON A CYLINDER OF A PRINTING PRESS, SAIDPLATE CONSISTING ONLY OF TWO LAYERS, ONE OF SAID LAYERS BEING A FLEXIBLERUBBER LAYER AND THE OTHER BEING A BACKING LAYER OF A DIMENSIONALLYSTABLE FLEXIBLE NONWOVEN SHEET PLASTIC MATERIAL, SAID LAYERS BEINGINTERFACIALLY BONDED, SAID RUBBER LAYER HAVING A PRINTING PATTERN INRELIEF ON ITS EXPOSED FACE, SAID PLATE, IN ITS UNSTRESSED CONDITIONPRIOR TO APPLICATION TO A CYLINDER HAVING A CURVATURE GENERALLYCORRESPONDING TO THAT OF THE CYLINDER WITH THE PRINTING PATTERN ON THECONVEX FACE OF THE PLATE.